After reading several posts about important modifications to make it seems changing out the stock exhaust is very close to the top of the list. Not knowing much about all  the parts and their names (down pipes, cat-backs, etc.), I was wondering if someone had a simple explaintion of each of the components and their relationship with one  another. Starting at the engine there is a manifold or header and the turbo hooks on somewhere up there. What's next, the down pipe, then the cat-back? I suppose after  that is some piping to the muffler and then finally the tail pipe, is that correct?

 If one was to invest in an upgraged performance exhaust system, doesn't other components such as air intake also have to be addressed? Seems like if you are going to  have the exhaust exit out more easily and in larger quantities, that the air also must enter the air box in greater quantity also other wise you would be starving the engine and the desired increase in HP could turn out to be a decrease instead. Is this correct thinking?

 Do you need a specialist to analyze the system for best results or can the do-it-yourselfer make these system changes?
 --
 Jim N Phx; 1996 855 TLA, 1992 965

 Here goes.

 Starting from the exhaust ports of the engine, the first part of the exhaust is the exhaust manifold. From the manifold, the following part is the exhaust side of the
 turbocharger. From there, the exhaust hits an impeller at a perpendicular axis to the flow from the exhaust manifold, and is then routed to another straight path. From
 here, the following piece of exhaust is called the downpipe. Late in the section of the downpipe, you will find the first O2 sensor. This sensor is found about 3/4 the way  down from the turbo, to the catalytic convertor, which is the next section of exhaust. From there, the remaining section is often called the cat-back; shortened from  catalytic convertor back. About two feet back from the catalytic convertor, you will find the second O2 sensor. The cat-back usually denotes everything after the cat, which is most cases refers to the piping and a single silencer.

 Yes, when you can evacuate gasses at a higher rate, it would be desirable to be able to ingest more gasses. So a higher flowing air filter will help. BUT, the biggest
 reason a high flowing exhaust helps on a turbocharged car is because it not only allows gasses to escape faster, it allows the turbocharger to spool up quicker and to
 higher rpm's. With less back pressure, the turbocharger spools quicker, and with higher flow rate, the turbocharger will spin faster.

 For naturally aspirated engines, a certain amount of back pressure is required. When the required back pressure is insufficient, the engine will actually lose power. This  occurs because as exhaust gasses flow away from the engine, they create a low pressure region in its wake. When this occurs, the following exhaust pulse uses this  negative pressure to help draw the successive exhaust pulse out. If the flow is too high, which can be created by running too large piping, or too short exhaust length, this will not occur, or to a lesser extent.

 With turbocharged cars, the turbocharger already acts as quite a restriction. And because the intake charge (when under positive pressure i.e. boost) is forced, as
 opposed to drawn in by a natural vaccuum as with naturally aspirated engines, the greatest preformance increase will be found with having the turbocharger spool faster  both in terms of response and in terms of rpm.

 As for deciding on piping size, thanks to many pioneers in modifying the 850, a number of piping diameters have already found to be most beneficial for the application  desired. For example, on a sub 275hp 850T engine, a 2.5" cat-back is adequate. However, for a 300hp+ 850T, one will require ATLEAST a 3" downpipe, and a 2.5"  cat-back. And if one is willing to trade some high rpm end power for some low end torque, a full 3" system would be most desirable, and will easily be good for 350hp. It  all depends on how far you go, and how much of a noise increase you are willing to live with.

 At first, I had a 3" downpipe, a 3" race-cat, and a 2.5" cat-back installed with one silencer. The silencer I used was heavily geared for performance over sound absorption.  As a result, it was REALLY loud for an 850. It hauled butt, but it was noisy. After a while, due to complaints from others who had driven the car, I switched to a 3" system  with 2 silencers. The first things I noticed was a deepening in the exhaust tone, and a significant decrease in noise. I even picked up about 2-3hp and about 1-2 ft.lbs of  torque after switching systems, while also decreasing noise as well as deepening the exhaust tone. I absolutely love the sound of the car now. When I run through 2 or 3  gears at full throttle, the car is absolutely gorgeous in the way it pulls and in the noises it makes. I have a recording of my car with the first system, and I after comparing  it too the system I have now, I love it even more. The first system had a more raw and carnal grunt, the system I have now sounds much more tuned and refined.

 A word of caution, every single silencer and cat, will sound differently. Even though they may have the same external size, design, etc, you will hear a difference. Heck,  even the cat and the thickness of the piping will affect the sound of the exhaust.

 Currently, I am running a custom made 3", T-304 stainless steel downpipe, a Random Tech 3" internal diameter cat, a custom made T-304 3" cat-back, a polished 3"  internal diameter Saber straight through (non-baffled) silencer mounted in the stock location, and a polished T-304 stainless steel Vibrant Performance silencer. I paid a  little more to have a polished rear mount and tip, and to have everything made in stainless steel, but I think it was worth it. To get an exhaust like this, the average is  about $1500 Canadian or about $925 US after all the taxes and labour and parts. A cat-back should cost you about $750 or less.

 About the only drawback I've faced so far is that my car has a tendency to run rich under repeated partial throttle for extended periods of time, i.e. stop and go traffic. This  occurs because the EGR is not operating as it should as the stock ECU is not fully taking the increased flow into account. I am getting a custom ECU made for my car  at the end of the month, and that should take care of the problem. So far, no codes have been set, and besides having a little more difficulty in installing the thicker iPd  anti-roll bars I have sitting in my garage right now, there have been no adverse affects. The front anti-roll bar sits VERY close to the downpipe, so I may have to do some  exhaust allignment adjustments when I try to install the iPd bars.

 Hope this helped.
 --

 Sin, you have done a very nice job of explaining, Thanks! As with any thing being learned I have some more questions in response to what you wrote.

 So is there a "header" on the 850's that attaches to the exhaust manifold?
 Or is that something only for non-turbo engines?

 I see that iPd sells a "Sport Exhaust System". Isn't that nothing more than the cat-back? I assume it must be something less than 2.5" to fit directly onto the stock cat,
 right?

 What sizes are the stock exhaust system and is there any difference between the 850 Turbo and the 850 R systems?

 If I wanted to do an upgrade in stages, could I install just the 3" cat-back first with 2 silencers? Would there be any fit up problems mating to the stock cat?

 Did you use the existing O2 sensors or do they have to be upgraded (I don't know how they mount - if I did maybe this question wouldn't have been asked)?

 With a complete 3" system now are you considering going to a bigger turbo?

 Thanks again for all the great information!
 

 --
 Jim N Phx; 1996 855 TLA, 1992 965

 A header is a synonym for exhaust manifold.

 iPd's "Sport Exhaust System" is a 2.5" cat-back. The stock piping diameter averages 2.25". I say average because much of the piping isn't mandrel bent. And no, there  is no exhaust difference between the 850T and the 850R exhaust. In later model R's (_70), dual exhausts were available, and dual exhausts can be retrofitted to 850T's.

 It is not wise to go from a high restriction 2.5" cat directly to a 3" cat-back. The surface area of 2.25" pipe is about 3.976078202" squared, and when you consider the  surface area that is taken up by the ceramic catalytic internals, that number drops significantly. A 3" pipe will have a surface area of 7.068583471" squared. This is a  HUGE difference. The best exhaust systems will evacuate the exhaust as quickly as possible. And when a gas goes from a piping of 2.25" to 3", the flow of gas RAPIDLY slows down and cools. Both are bad things for an exhaust. You want the exhaust charge to stay as hot as possible, travelling as rapidly as possible.

 In essence, you will gain less with a 3" cat-back then you will with a 2.5" cat-back, if you keep the rest of the exhaust stock.

 As for going from one size of piping to another, it really isn't that hard. Basically, you weld on an adapter flange of piping to both ends.

 Sorry about not mentioning the O2 sensors. That just slipped my mind. Basically, they drilled a hole in the piping, and welded on a tapped nut so that the sensor can
 simply screw into the piping. This is basically how the O2 sensor is bolted to the stock exhaust.

 I am considering stepping up to a larger turbo, but that may not be necessary. I am already pulling aobut 260hp and 260 ft.lbs of torque at the engine. When I get a
 custom made chip at the end of the month, I should be around the 300hp 300ft.lbs area. From what I've read, the stock internals (most importantly) the connecting rods,  begin to bend and snap. Other things I must upgrade if I want to go beyond 300hp/ft.lbs is injectors. At over 300hp/ft.lbs, the stock injectors don't dump enough fuel, thus  leading to running lean, which can melt your pistons. With the stock mitsu 15G turbo, the car will easily produce 300hp/ft.lbs. After that, the biggest concerns are the  connecting rods, injectors and transmission. As the con rods and the tranny are things I don't plan on modifying, I will be content with 300hp/ft.lbs. So I see no need to  upgrade the turbocharger. The 15G will run within it's optimal thermal efficiency right up to about 325hp. After that, the thermal efficiency drops right off the table. If I get a  chance, i.e. find a 16G or even 18G off of a wrecked car, I'll probably snap it up, but unless I do, I am content with the stock 15G turbo.

 Any more questions? :)
 --

 A bit optimistic on the 325 HP limit on a completely unmolested 15G but it's all moot like you said--the inline 5 can really only handle 300 HP before it starts choking on  itself. You'll be looking for a 16T or 18T Mitsu turbo off those S70s--it shouldn't be too hard locating one in TO considering even I managed to snap one up recently here in  Van.

 Questions, hehehe, I gots more. Sorry :>)

 "the piping isn't mandrel bent" - I don't understand the significance of this statement. Can you please explain?

 Looking in the phone book for exhaust shops I see many of the ads boast about "sound" and "dual conversions" and "glasspacs". At the other end of the spectrum I see  Meineke and Midas volume discount pricing. So how do you go about finding a shop that knows Volvo turbos and just doesn't hang mufflers on cars? Should I only deal  with the ones that specifically mention they are custom and have 3" exhaust systems?

 What about emission problems resulting for the upgrading of an exhaust system - I assume as long as you keep the gasses moving down the pipe quickly you won't have  problems passing the state emissions tests, right?

 What are the quality brands for the components to consider? I'm assuming that if a shop carries the quality stuff, I will less likely have a pile of rusted and burned out
 pipes under my car after a couple of years that once was called a performance exhaust system.

 Is T-304 Stainless Steel really necessary if you don't live in the rust belt? Ya know, Arizona has a dry heat! :>)

 Well thanks again.
 --
 Jim N Phx; 1996 855 TLA, 1992 965

 If you care about getting good performance, mandrel bending is important. Mandrel bending is bending the pipe such that the cross sectional area remains a perfect
 circle, as opposed to be distorted to an elipse, which has a smaller cross sectional area, which also has poorer flow characteristics.

 Well, I have a feeling the "sound" is for those that are looking to change the sound of their exhaust. For example, my 855T now sounds much deeper and more refined. A  "dual conversion" will be for those that have a single pipe and want a dual exhaust outlet. The majority of the time, this occurs right at the very end of the exhaust stream,  so it makes little to no performance difference. "Glasspac" is something used in mufflers for silencing. Imagine I took a 3" pipe and punched regularly spaced holes  throughout the piping for about 14". I then put an 8" pipe around it. I then packed the glasspac (basically a form of fibreglass) between the inner 3" pipe and the outter 8"  pipe, then sealed both ends. This is now a straight through silencer. As for Meineke and Midas, these places don't do custom performance exhaust work. They don't  mandrel bend their piping, use baffled silencers as opposed to straight through. I recommend going to a shop that specializes in high performance exhaust work. They  use mandrel bent tubing, are experienced with dealing with clearance issues with using larger then stock piping, as well as performance friendly such that when you  decide to do other mods which might conflict with the ones you already have, they are usually happy to help out.

 As for emissions, as long as you use a certified catalytic convertor, run both O2 sensors in the stock locations, and a silencer that silences enough, you will meet all
 emissions and sound level laws. Like I said, I have a 3" downpipe back system, and I have yet to throw a light.

 As for quality brands, I like Random Tech for their cats, but they are probably the most expensive. I've tried Vibrant Performance before and both in performance, and  appearance both internal and external, without the Random Tech logo, you can't tell the difference between the two, and the Vibrant Performance cat is WAY cheaper. As  for piping, it's basically all the same, but you may want to compare the piping used between shops. I found that the shop I used had slightly thicker piping, so I was  pleased with that.

 If you are really concerned with "I will less likely have a pile of rusted and burned out pipes under my car after a couple of years that once was called a performance
 exhaust system" then get T-304 stainless steel. It's that simply, it's either dry enough (no road salt usage) that you don't have to worry about rust, or you don't. BTW,  short drives whether in cool or hot temperatures are even larger reasons for exhausts rusting out. Other things to consider are the quality/purity of the gasoline available to  you. I know, in Canada, our gas has a MUCH higher sulphur content then it does in the US. So just because you don't get a lot of moisture or road salt or sea salt,  doesn't mean your exhaust won't rust. The sulphur in the gasoline enters the exhaust stream in particulate form, and when dissolved in the condensed water that has  condensed on the insides of the piping, becomes sulphuric acid, and acids rapidly accelerate rusting. That's why exhausts rust from the inside out.

 Put it this way, if you go with a T-304 exhaust, you will never ever have to replace your exhaust. It will DEFINETLY outlive your car. If a full T-304 exhaust goes for $1500  Canadian, then a full aluminized steel exhaust at the cheapest, will cost $1000 Canadian. Yes, that's 1/3 cheaper, but I think it's worth it. But then again, it depends on  your driving habits, your climate, and how long you plan on keeping your car.
 --

 Thanks Sin for a really well written story on performance exhaust systems for the 850 !

 Perhaps Mike at Ozbrick.com should consider compiling the your several posts into one complete story.

 Sin you have really nailed it. I've run out of questions!!! :>) You have given me enough "exhaust smarts" that I now feel comfortable talking with the custom shops and  understand what they will be telling me.

 Thanks so much for sharing your wealth of information with me and the rest of the BB. I'd say that this one will be a classic.
 --
 Jim N Phx; 1996 855 TLA, 1992 965

 I really appreciate your compliments. I'm just glad I could help you guys out.

 I'm a real performance enthusiast, and with my current car being an 850, I can't get enough of performance enhancing on the 850. I just love it when I see another modified
 850.

 Keep moding guys.
 --

 Nathan,

 I have discovered this excellent thread (just in the nick of time) and will archive it on my site - but I fear some others re. exhaust have slipped by me, as I'm not always able to tune into the brickboard. If anyone has any discussions archived & wants to see them on Ozbrick, just email them to me.
 cheers

 --
 Michael.

 I know IPD and Wett always advertise their performance upgrade as a package but if you could only upgrade in stages (due to $$ restraints), which would you upgrade
 first? Sport Dual Exhaust or Chip (and if I do it in stages, does it matter if I go with IPD or Wett?)

 I read some time ago from Mike Harris of SanDiego that he upgraded with Wett chip and then exhaust, after a while, he simply replaced the stock ECU chip back, I like
 to know the reason why? Mike if your radar is on and can pick this up, I appreciate your input.

 JT-

 I currently have neither, but if you read the blurb in IPDs catalog - "The TME website specifies that when the ECU is upgraded that the sport exhaust must be installed to
 prevent damage to the turbo under extreme loads". They then go on to state they don't think you'll ever load your turbo that extremely.

 That being said, when I do upgrade my T5, I will probably go the route of exhaust first, then ECU. Hey, I'm a stress analyst, and I tend towards being convervative...
 --
 1998 S70 T5M, 1983 245 rustbucket DL
 

 exhaust
 went to a local speedshop got a 2.5 inch cat-back with flowmaster & resonator installed for about $210.00 out the door

 don't live in the rust belt, so I don't really care if it's not stainless

 This answer should be a unanimous "EXHAUST".

 Do your exhaust (I went with a SuperSprint), then K&N, then ECU, then Magnecors, then....

 You get the idea.

 -JP
 --
 T-5 M, iPD ECU, SuperSprint Exhaust, iPD Anti-sways, Magnecores, K&N, etc... :-)
 
 

                                                         My volvo page

 JT-anyone who is a "real" enthusiast(spell??) knows that Torque is the name of the game. And that is what better breathing(aka less restrictive exhaust and bigger intake)
 will get ya. The ECU will only, i believe, increase boost, fuel, etc. But it will not let ya engine breath better! that's why I would do a cat-back & intake b/4 ECU and will be
 quicker off the line. Once up & running, then HP comes in and exos will give a few more ponies too.
 the thing is, what do ya do with a fairly good exos if you go the SS route. No one buys used stock exos, do they?? So, I wait till mine is somewhat old/bad/rusted, then I
 upgrade. good luck, BD
 --
 97854t5

 How did you insert that picture at the end of your post? I tried that a few months back and it wouldn't let me do it. I was using the typical cut and paste techniques.
 --
 Jim N Phx; 1996 855 TLA, 1992 965

 Jim:

 Do this: host your foto somewhere, anywhere, and know the path to it. Say it's www.members.yahoo.com/jim/850.jpg

 Then put this in the 'Optional Image URL' field below everything on the post page:
 http://www.members.yahoo.com/jim/850.jpg

 Getting the free space to host it is the hard part :)
 --
 Matthew de Seattle~~~black 97 854 T5 all options, few mods, 2 turns wastegate :-)

 Obviously, everyone will have their own take on this, but I went first with a K&N air filter, then the Wetterauer chip, and someday will probably put in the Volvo dual
 exhaust from the 2000 V70R. I just had a hard time justifying throwing away a perfectly good original exhaust system. I am very happy with the performance of my car as
 it now is. I'm sure the exhaust will make it even better............someday. The only minor glitch with the chip is an occasional stumble, but it is hardly noticeable most of
 the time. I'm not sure if the ipd ecu does that also; I haven't heard anyone mention it.
 

 --
 Gordon - 86 240 DL; 99 Honda Odyssey; 98 XC with Wetterauer chip (230 HP, 258 ft-lbs), ipd sway bars, ipd skid plate, SC-900 radio & amp